[unreadable] Cannabis is the most widely used illicit substance among adolescents; however, the long-term neural consequences of chronic use are relatively understudied. The effects of cannabis on brain structure have yielded inconsistent results, as some have found differences in brain volume and others have not. Studies examining the cognitive effects of chronic cannabis use have primarily demonstrated subtle deficits in memory and attention. Of concern is that the current literature lacks studies that adequately assess the effects of cannabis exposure in adolescents during the critical period of neuromaturation. Therefore, the goal of this project is to examine whether cannabis use during late adolescence is associated with long-lasting brain structural changes, measured by magnetic resonance imaging (MRI), and neuropsychological functioning. Gender will also be explored as a potential moderator variable between brain structure, neuropsychological functioning, and cannabis use. Data will be collected from two groups of 16-18 year old adolescents: 1) Cannabis users and 2) Non-drug using controls who have verified 28-days of abstinence. Based on animal models and existing data in humans, it is hypothesized that cannabis use will be associated with decreased brain volume in prefrontal and cerebellar regions and poorer cognitive performance on tests of learning and memory, working memory, attention, executive functioning, and psychomotor speed. [unreadable] [unreadable] [unreadable] [unreadable]